The present invention relates to an apparatus and method for comminuting coral limestone, and specifically relates to the use of a waterbox having an overflow weir disposed above the feed assembly of a conical crusher so as to create a controlled water/coral limestone slurry and to introduce such slurry into the crushing cavity of the conical crusher.
Coral limestone is a variety of limestone which is mined in the Southeastern portion of the United States, principally in Florida. Coral limestone is crushed and sized for use in various construction operations, such as aggregate for concrete structures, roadbeds and drainage fields. These uses for coral limestone require the particles to be cuboidal in shape for optimum results.
Up to the present time, coral limestone could not be crushed successfully in a conical crusher, normally employed as either a secondary or tertiary crusher in a comminution circuit, due to the buildup of wet fines on the mantle, bowl liner and feed chute surfaces The wet fines form a paste-like substance which may accumulate to the extent that no discharge of crushed product can take place. This paste-like substance which clogs the crushing cavity is due in large part to the 8-9% moisture level of the coral limestone as it is taken from the ground. Accordingly, conical crushers have generally not been used to crush coral limestone.
Conventional attempts to solve the problem of comminuting coral limestone involve the use of horizontal shaft impactor crushers after the material has been stockpiled to allow excess water to drain off. This method is less than satisfactory because the horizontal shaft impactor produces more fines at a higher operating cost and thus is inherently less efficient than a conical crusher.
Commonly assigned U.S. Pat. Nos. 4,750,679 and 4,671,464 disclose an apparatus and method for injecting water into the crushing cavity of a conical crusher and adjustments to the crusher to produce a flakier product which is easily and more efficiently ground in a mill. In "Crushing Under Water Flush", by Karra, Engineering and Mining Journal, May, 1982, pp. 103-106, the creation of a low (4%) solids content limestone slurry in a jaw crusher is discussed, and high solids content slurries, i.e., more than 60% solids, are described as being less energy efficient than crushing without water. In addition, low solids content mineral slurries are commercially undesirable due to the high cost of handling and preparing a final commercial product from the crushed product.
Consequently, there is a need for a mechanism enabling the efficient use of a conical crusher in the comminution of coral limestone. Such mechanism should enable the conical crusher to produce a relatively large volume of cuboidal products of the type desired for construction grade aggregate, and should minimize or eliminate the buildup of wet fines in the crusher.